In switching a radio transmitter on and off, so-called spectrum spreading occurs, i.e. the transmitted frequency spectrum is considerably wider than for continuous transmission. Spectrum spreading therefore occurs in such as time multiplexed mobile telephony systems, since the transmitted power from each mobile station goes down to zero after each time slot. The spectrum spread can thus cause noise in channels utilizing other frequencies.
Spectrum spreading occurs in the use of frequency-jumping equipment also. It is known to reduce such spectrum speading by utilizing an RC network in a regulating loop for controlling the output power of the final stage. Here the output power is controlled such that it increases from zero to a maximum value during a time interval immediately after each frequency jump, and vice versa immediately before each frequency jump. The decrease in spectrum spreading is dependent on along what imaginary curve the output power is increased or decreased. This curve is in turn dependent on the complexity of the RC network and thereby also to the cost of the network.
It is conceivable to utilize a similar technique for reducing the spectrum spread in a time multiplexed radio transmission system e.g. a mobile telephony system. In practice, however, it would not be possible to achieve sufficient spectrum attenuation for such a system with the aid of an RC network according to the above, with retention of reasonable complexity of this network and thus the cost of it.